LinkedHashMap与不同类型的数据

Question

I have a LinkedHashMap

My code

LinkedHashMap<String, String> hmap = (LinkedHashMap<String, String>)data[0];

System.out.println("Contents of LinkedHashMap : " + hmap);

System.out.println("\nValues of map after iterating over it : ");


for (String key : hmap.keySet()) {
     System.out.println(key + ":\t" + hmap.get(key));
  }

Output:

Values of map after iterating over it : cd: PARB id_inst:PE103AA01 cd_anul:

Error calling method: generateReport

java.lang.ClassCastException: java.lang.Double cannot be cast to java.lang.String

Contents of LinkedHashMap:

{cd=PARB,id_inst=PE103AA01, cd_anul=, mnt=276562.5, dt_den_theo=2012-01-24 00:00:00, logo=PARB.bmp, id=ISI.model.ParamRecord-1}

How can I use String and Double in my Hashmap without LinkedHashMap<String, Object> ?

Answer 1

我不确定您的代码是否具有通用类型<String, Object> ，如果没有，则for (String key : hmap.keySet()) {应该存在编译错误，否则，它会很好地工作。

Answer 2

Your issue is not that LinkedHashMap can't contain both String and Double instances. It actually perfectly can. The issue is what you are doing with those values when you iterate the list. If you try to use the value as a String while it is Double you will get ClassCastException. If all you need is a String instance regarding of the actual object class you could call toString() to convert it like this:

Object o = hmap.get(key);
String stringVal = (o == null) ? null : o.toString()